I believe ths is the page you are looking for. Below is quoted information from that page. Microsoft did move a lot of stuff around in Windows 7 compared to XP, so for the exact part of the window where you are finding registered file types, this will do.
To find the registered file types on a
computer running Windows Vista or
Click Start. Open Control Panel, click Control Panel Home in Windows
Vista, and click Programs.
Click Default Programs, and click Associate a file type or protocol with
On this screen, the registered file types are displayed.
For more information about how to
change the file types, files, and
folders that are migrated when you
specify the MigUser.xml file, see
Below is a screenshot of the window.
It seems that the first part did not work. Here is a way that is supposed to work. I did not test it, I just read a lot about it. This page showed a couple ways of completing the desired task. Both ways unfortunately require purchasing a program.
You might be able to download the free trial and change only what you want and uninstall the program. Hopefully that would cause the changes to be permanent due to the program making registry changes.
Please note that I am only trying to name easy ways.